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JERUSALEM, Israel (CNN) - The US officially relocated its Embassy to Jerusalem on Monday, formally upending decades of American foreign policy in a move that was met with clashes and protests along the Israeli-Gaza border.

At least 43 Palestinians were killed in Gaza as deadly protests took place ahead of and during the ceremony in Jerusalem — making it the deadliest day there since the 2014 Gaza war.

President Donald Trump did not attend the ceremony in Jerusalem's Arnona neighborhood, but in a video message broadcast at the event he congratulated Israel, saying the opening had been "a long time coming."